The use of conductive adhesives are well known in many electrical applications to connect an electrical component to a circuit, particularly to a circuit board having conductive paths in some sort of pattern. Once properly secured, current passes between the electrical component and the conductive path through the conductive adhesive. Such adhesives were developed to replace soldering techniques. Soldering requires spot application whereby depositing of the solder must be precisely controlled and is very difficult with developing micro-electronics. In addition, soldering requires specific temperature resistant components and substrates.
One example of an electrically conductive adhesive which has been developed embodies a nonconductive resin or base having randomly spaced conductive particles therein. The particles are elongated, as in strand or fiber configurations, whereby the adhesive is conductive in the longitudinal direction of the fibers but nonconductive in a direction transverse to the fiber direction. Often, the fibers are magnetically oriented as appropriate for a given application.
Another example of a type of conductive adhesive is where the conductive particles are of a given size sufficiently large to span a predetermined gap between the electrical component and the conductive path. In other words, the particles are spaced a distance greater than the gap whereby when pressure is applied between the electrical component and the conductive path, the particles make contact therebetween but still remained sufficiently spaced parallel to the gap to establish only uniaxial conduction. All of these types of adhesives often are called "Z-axis" adhesives.
A further type of conductive adhesive is shown in U.S. Pat. Nos. 4,667,401, dated May 26, 1987, and 4,720,740, dated Jan. 19, 1988, both to Clements et al. These patents disclose the use of conductive adhesives which rely on a particular concentration of conductive particles in a nonconductive resin whereby upon the application of pressure between the electrical component and the conductive path on a substrate, the particles are moved together in the Z-axis direction, with the resin between the electrical component and the conductive path sort of being "squeezed out" in the X and Y directions so that electrical contact is made between the electrical component and the conductive path through the pressure concentrated conductive particles in the adhesive.
One problem with using some of the conductive adhesives as described above, such as in the above patents, is that extraneous components must be used to apply pressure between the electrical component and the conductive path in the Z-axis direction in order to establish conductivity through the adhesive in the pressure zone. Fixtures must be set up for applying the pressure, and the pressure must be maintained during cure. These procedures are expensive in both the cost of the fixtures and the time required to maintain the external fixturing during adhesive cure. In addition, with the ever increasing miniaturization of electronic devices, fixturing becomes extremely difficult if not impossible.
This invention is directed to a novel electronic device using pressure-sensitive conductive adhesive and which involves internal fixturing in the device itself to completely eliminate any external pressure-applying fixtures.